Semiconductor devices are widely used for integrated circuits for electronic applications, including radios, televisions and personal computing devices, as examples. Such integrated circuits typically include multiple transistors fabricated in single crystal silicon. It is common for there to be millions of semiconductor devices on a single semiconductor product. Many integrated circuits now include multiple levels of metallization for interconnections.
The manufacturing process flow for semiconductors is generally referred to in two time periods: front-end-of-line (FEOL) and back-end-of-line (BEOL). Higher temperature processes are typically performed in the FEOL, during which impurity implantation, diffusion and formation of active components such as transistors are performed on a semiconductor substrate of a wafer. Lower temperature processes usually take place in the BEOL, which is generally considered to begin upon the formation of the first metallization layer on the wafer.
Capacitors are elements used extensively in semiconductor devices for storing an electric charge. Capacitors essentially comprise two conductive plates separated by an insulator. The capacitance, or amount of charge held by the capacitor per applied voltage, is measured in farads and depends upon a number of parameters such as the area of the plates, the distance between the plates, and the dielectric value of the insulator between the plates, as examples. Capacitors are used in filters, in analog-to-digital converters, memory devices, and control applications, and many other types of semiconductor devices.
One type of capacitor is a MIMCap, which is used frequently in mixed signal devices and logic devices, for example. MIMCap's are used to store a charge in a variety of semiconductor devices, such as mixed signal and analog products. MIMCap's typically require a much lower capacitance than deep trench memory capacitors used in dynamic random access memory (DRAM) devices, for example. A MIMCap may have a capacitance requirement of 1 fF/micrometer2, for example.
Recently, there has been an increase in demand for MIMCap's embedded in BEOL integrated circuits. MIMCap's typically are horizontal MIMCap's comprising two metal plates that sandwich a dielectric parallel to the wafer surface. Prior art horizontal MIMCap's are usually manufactured in the BEOL by forming the bottom capacitive plate in the first or subsequent horizontal metallization layer of a semiconductor wafer. A capacitor dielectric is deposited over the bottom capacitive plate, with a second mask, pattern and etch step being required to form the top capacitive plate.
Alternatively, MIMCap's may be formed between horizontal metallization layers in the BEOL in additional horizontal layers, with each plate requiring a separate pattern and etch level.
A horizontal MIMCap requires a relatively large amount of surface area on a semiconductor wafer. A horizontal MIMCap is a large flat capacitor positioned parallel to the wafer surface covering a large area of the chip, and therefore, MIMCap's do not provide a high area efficiency. As the demand for the capacitance increases, it is desirable to develop MIMCap's that utilize the chip area as efficiently as possible.
A vertical MIMCap, described in patent application Ser. No. 09/742,918 for “Self-Aligned Double-sided Vertical MIMCap”, incorporated herein by reference, discloses a vertical MIMCap structure and method that improves the efficiency of the use of chip surface area. Patent application Ser. No. 09/977,004 for “Vertical/Horizontal MIMCap Method”, also incorporated herein by reference, describes another way of manufacturing a vertical MIMCap. Vertical MIMCap's are advantageous in that they may be formed in the same inter-level dielectric as metal leads in a metallization layer, saving semiconductor surface area.